Update charted to 0.4.8 and roll

packages/barback/lib/src/asset/asset_node.dart

Index: packages/barback/lib/src/asset/asset_node.dart
diff --git a/packages/barback/lib/src/asset/asset_node.dart b/packages/barback/lib/src/asset/asset_node.dart
index 45d1b1771c215f165a2e3c001afb4a7ee5715e00..a9e000092d74681e52840bee14660d01ff130ac7 100644
--- a/packages/barback/lib/src/asset/asset_node.dart
+++ b/packages/barback/lib/src/asset/asset_node.dart
@@ -8,7 +8,6 @@ import 'dart:async';
 
 import '../errors.dart';
 import '../graph/transform_node.dart';
-import '../utils.dart';
 import 'asset.dart';
 import 'asset_id.dart';
 
@@ -84,7 +83,7 @@ class AssetNode {
   /// The return value of [callback] is piped to the returned Future. If the
   /// asset is removed before becoming available, the returned future will throw
   /// an [AssetNotFoundException].
-  Future whenAvailable(callback(Asset asset)) {
+  Future/*<T>*/ whenAvailable/*<T>*/(/*=T*/ callback(Asset asset)) {
     return _waitForState((state) => state.isAvailable || state.isRemoved,
         (state) {
       if (state.isRemoved) throw new AssetNotFoundException(id);
@@ -115,9 +114,9 @@ class AssetNode {
   /// [callback] is called synchronously if this is already in such a state.
   ///
   /// The return value of [callback] is piped to the returned Future.
-  Future _waitForState(bool test(AssetState state),
-      callback(AssetState state)) {
-    if (test(state)) return syncFuture(() => callback(state));
+  Future/*<T>*/ _waitForState/*<T>*/(bool test(AssetState state),
+      /*=T*/ callback(AssetState state)) {
+    if (test(state)) return new Future.sync(() => callback(state));
     return onStateChange.firstWhere(test).then((_) => callback(state));
   }